1. Technical Field
The present invention relates to a pilot-operated safety valve assembly and more particularly to a safety valve assembly suitable for a hydraulic overload protector of a mechanical press.
2. Description of Prior Art
There is a conventional safety valve assembly which is recited in Japanese Patent Publication No. 54-23474 the present inventors previously proposed, as an example of the safety valve assembly of this type.
The conventional safety valve assembly comprises a cylindrical main valve member brought into butting contact with a pilot valve member urged by a pushing spring for setting a safety operation pressure. The butting portion of the main valve member constitutes a relief valve seat.
In order to immediately reduce an abnormally increased pressure of fluid, it is necessary to enlarge a maximum relief amount at the time of a safety operation.
However, the safety valve assembly of the conventional structure has only one relief valve seat. Therefore, a trial to enlarge the maximum relief amount increases a sectional area of a hole of the relief valve seat to result in enlarging a pressure receiving area which starts the pilot valve member opening. And fluid pressure acting on the pressure receiving area determines a pushing force of the pushing spring. Accordingly, it is required to adopt a strong and large one for the pushing spring, which results in enlarging the safety valve assembly.